The present invention relates to an insulating-film-forming composition, a method of producing the same, a silica-based insulating film, and a method of forming the same. More particularly, the invention relates to an insulating-film-forming composition suitably used for an interlayer dielectric for semiconductor devices or the like, a method of producing the same, a silica-based insulating film, and a method of forming the same.
A silica (SiO2) film formed by a vacuum process such as chemical vapor deposition (CVD) has been widely used as an interlayer dielectric for semiconductor devices and the like. In recent years, a coating-type insulating film called a spin-on-glass (SOG) film containing a tetraalkoxysilane hydrolyzate as the major component has also been used in order to form an interlayer dielectric with a more uniform thickness. Along with an increase in the degree of integration of semiconductor devices, a low-relative-dielectric-constant interlayer dielectric called an organic SOG film containing a polyorganosiloxane as the major component has been developed.
However, more excellent electrical insulation between conductors has been demanded accompanying a further increase in the degree of integration and the number of layers of semiconductor devices. Therefore, an interlayer dielectric exhibiting excellent storage stability, a lower relative dielectric constant, and higher mechanical strength has been in demand.
The manufacture of semiconductor devices involves a chemical mechanical planarization (CMP) step for planarizing an insulating layer and various washing steps. Therefore, a material used for an interlayer dielectric or a protective film for semiconductor devices is required to exhibit mechanical strength and chemical resistance against chemical corrosion in addition to dielectric constant characteristics.
As a material exhibiting a low relative dielectric constant, a composition containing fine particles obtained by condensing an alkoxysilane in the presence of ammonia and a basic partial hydrolyzate of an alkoxysilane (JP-A-5-263045 and JP-A-5-315319), and a coating liquid obtained by condensing a basic hydrolyzate of a polyalkoxysilane in the presence of ammonia (JP-A-11-340219 and JP-A-11-340220) have been proposed. However, the material obtained by the above method is not suitable for industrial production since the reaction product exhibits unstable properties and the resulting coating shows a large change in relative dielectric constant, crack resistance, mechanical strength, adhesion, and the like.
A method of forming a low-dielectric-constant insulating film using a coating liquid prepared by mixing a polycarbosilane solution and a polysiloxane solution has also been proposed (JP-A-2001-127152 and JP-A-2001-345317). However, this method has a problem in that the carbosilane domains and the polysiloxane domains are unevenly distributed in the resulting coating.
A method has also been proposed which uses an organosilicate polymer obtained by hydrolysis-condensation of a carbon bridge-containing silane oligomer prepared from an organometallic silane compound (WO2002-98955). However, a material obtained by this method cannot be stored for a long time due to poor stability of the reaction product. Moreover, this material exhibits poor adhesion to a substrate.
A method of forming a low-dielectric-constant insulating film by hydrolysis-condensation of a highly branched polycarbosilane has been proposed (U.S. Pat. No. 6,807,041). However, since aging using ammonia, trimethylsilylization, curing at a high temperature of 500° C., and the like are required after applying the polymer to a substrate, this method is not suitable for practical use.